HomeMy WebLinkAboutSW8050410_COMPLIANCE_20190405STORMWATER DIVISION CODING SHEET
POST -CONSTRUCTION PERMITS
PERMIT NO.
SW�
DOC TYPE
❑ CURRENT PERMIT
❑ APPROVED PLANS
❑ HISTORICAL FILE
COMPLIANCE EVALUATION INSPECTION
DOC DATE
YYYYMMDD
DETENTION POND ANALYSIS FILENAME: G:\DATA\WPDATA\WQS\POND1050410.WKI
PROJECT#: SW8 050410 REVIEWER: P.Bartlett
PROJECT NAME: Midway Station
DATE: 1 9-Apr-05
Receiving Stream: Lockwoods Folly River Class: C; SW
Drainage Basin: Lumber River Index No. 115-25-1-(1)
Site Area 4.41 acres
Drainage Area :
square feet Area 4.41 acres
. I
IMPERVIOUS AREAS
Rational C
streets 10068.00 square feet 0.95
other on -site, future 162822.00 square feet 0.95
square feet
square feet
square feet
square feet
TOTAL 117299'0Qq-] square feet Rational Cc= 0.88
% IMPERVIOUS
90,00%
SA/DA Ratio
3.30%
Des. Depth
7.5
Req. SA
6339 sf
TSS:
90
Prov. SA
5538 sf
VOLUME CALCULATION * place a "I" in the box if Rational is used
Rational ?*
I
Des. Storm
inches
Rv=
0.86
Bottom
34.5
msI
Perm. Pool
i4
msI
Design Pool
44
msl
Design SA
9467
sf
Req. Volume
cf
Prov. Volume
MMI-8005:11
cf
ORIFICE CALCULATION
Avg. Head =
Flow Q2, cfs
Flow Q5, cfs
No. of Orifices
Diameter, inches
Drawdown =
0.97
ft
0,081
cfs
0.032
cfs
weir H x W
days
FOREBAY
Perm. Pool Volume=
Req. Forebay Volume=
Provided Volume=
Percent=
SA @
Elevation=
30622
6124.4
6585.00
Q2 Area = 2.46 sq. in.
Q5 Area = 0.99 sq. in.
Orifice Area 1.77 sq. in.
Q= 0,058 cfs
in x = in
COMMENTS
Surface Area , Volume and Orifice are within Design Guideline:
NKT #03075
Permit No. SGJf 0,('-llV1 D
State of North Carolina (to be provided by DWQ)
Department of Environment and Natural Resources
Division of Water Quality
STORMWATER MANAGEMENT PERMIT APPLICATION FORM
WET DETENTION BASIN SUPPLEMENT
This form may be photocopied for use as an original
DWQ Ston-nwater Management Plan Review:
A complete stormwater management plan submittal includes an application form, a wet detention basin
supplement for each basin, design calculations, and plans and specifications showing all basin and outlet
structure details.
I. PROJECT INFORMATION
Project Name: Midway Station
Contact Person: Phil Norris, P.E. Phone Number: (910) 343-9653
For projects with multiple basins, specify which basin this worksheet applies to: 1
elevations
Basin Bottom Elevation 34.50 ft. (floor of the basin)
Permanent Pool Elevation 42.00 ft. (elevation of the orifices)
Temporary Pool Elevation 44.00 ft. (elevation of the discharge structure overflow)
areas
Permanent Pool Surface Area 6,538 sq. ft. (water surface area at the orffice elevation)
Drainage Area 4.41 ac. (on -site and off -site drainage to the basin)
Impervious Area _ 3.97 ac. (on -site and off -site drainage to the basin)
volumes
Permanent Pool Volume
30,622
cu. ft.
(combined volume of main basin and forebay)
Temporary Pool Volume
16,005
cu. ft.
(volume detained above the permanent pool)
Forebay Volume
6,585
cu. ft.
(approximately 20% of total volume)
Other parameters
SAIDA'
0.033
(surface area to drainage area ratio from DWQ table)
Diameter of Orifice
1.5
in.
(2 to 5 day temporary pool draw -down required)
Design Rainfall
1.0
in.
Design TSS Removal 2
90
%
(minimum 85% required)
Form SWU-102 Version 3.99 Page 1 of 4
Footnotes:
1. When using the Division SA/DA tables, the correct SA/DA ratio for permanent pool sizing should be computed based upon the
actual impervious % and permanent pool depth. Linear interpolation should be employed to determine the correct value for non-
standard table entries.
2. In the 20 coastal counties, the requirement for a vegetative filter may be waived ifthe wet detention basin is designed to provide
90% TSS removal. The NCDENR BMP manual provides design tables for both 85% TSS removal and 90%TSS removal.
ld. REQUIRED ITEMS CHECKLIST
The following checklist outlines design requirements per the Stormwater Best Management Practices Manual
(N.C. Department of Environment, Health and Natural Resources, February 1999) and Administrative Code
Section: 15 A NCAC 2H .1008.
Initial in the space provided to indicate the following design requirements have been met and supporting
documentation is attached. If the applicant has designated an agent in the Stormwater Management Permit
Application Form, the agent may initial below. if a requirement has not been met, attach justification.
Initials
a. The permanent pool depth is between 3 and 6 feet (required minimum of 3 feet).
� _ b. The forebay volume is approximately equal to 20% of the basin volume.
1nn— c. The temporary pool controls runoff from the design storm event.
The temporary pool draws down in 2 to 5 days.
NJA e. If required, a 30-foot vegetative filter is provided at the outlet (include non -erosive flow
calculations.
The basin length to width ratio is greater than 3:1.
The basin side slopes above the permanent pool are no steeper than 3:1.
A submerged and vegetated perimeter shelf with a slope of 6:1 or less (show detail).
Vegetative cover above the permanent pool elevation is specified.
A trash rack or similar device is provided for both the overflow and orifice.
A recorded drainage easement is provided for each basin including access to nearest right-
of-way.
If the basin is used for sediment and erosion control during construction, clean out of the
basin is specified prior to use as a wet detention basin.
A mechanism is specified which will drain the basin for maintenance or an emergency.
M. WET DETENTION BASIN OPERATION AND MAINTENANCE AGREEMENT
The wet detention basin system is defined as the wet detention basin, pretreatment including forebays and the
vegetated filter if one is provided.
This system (check one) ❑ does ® does not incorporate a vegetated filter at the outlet.
This system (check one) ❑ does ® does not incorporate pretreatment other than a forebay.
Form SWU-102 Version 3.99 Page 2 of 4
Maintenance activities shall be performed as follows:
After every significant runoff producing rainfall event and at least monthly:
a. inspect the wet detention basin system for sediment accumulation, erosion, trash accumulation,
vegetated cover, and general condition.
b. Check and clear the orifice of any obstructions such that drawdown of temporary pool occurs
within 2 to 5 days as designed.
2. Repair eroded areas immediately, re -seed as necessary to maintain good vegetative cover, mow vegetative
cover to maintain a maximum height of six inches, and remove trash as needed.
3_ Inspect and repair the collection system (i.e. catch basins, piping, swales, riprap, etc.) quarterly to
maintain proper functioning.
4. Remove accumulated sediment from the wet detention basin system semi-annually or when depth is
reduced to 75% of the original design depth (see diagram below). Removed sediment shall be disposed of
in an appropriate manner and shall be handled in a manner that will not adversely impact water quality (i.e.
stockpiling near a wet detention basin or stream, etc.)
The measuring device used to determine the sediment elevation shall be such that it will give an accurate
depth reading and not readily penetrate into accumulated sediments.
When the permanent pool depth reads
When the permanent pool depth reads
Sediment Re oval El. 38.25 ✓ 75
Bottom El vation 37.00 _�
FOREBAY
5.63 feet in the main pond, the sediment shall be removed.
3.75 f feet in the forebay, the sediment shall be removed.
BASIN DIAGRAM
(fill in the blanks)
Permanent Pool Elevation 42.00
Sediment Removal Elevation 36.37 175% ✓
\ Bottom Elevation 34.50 25%/
uEVIZO9410 7
5. Remove cattails and other indigenous wetland plants when they cover 50% of the basin surface. These
plants shall be encouraged to grow along the vegetated shelf and forebay berm.
6. If the basin must be drained for an emergency or to perform maintenance, the flushing of sediment through
the emergency drain shall be minimized to the maximum extent practical.
Form SWU-102 Version 3.99 Page 3 of 4
.f. f
7. All components of the wet detention basin system shall be maintained in good working order.
I acknowledge and agree by my signature below that I am responsible for the performance of the seven
maintenance procedures listed above. I agree to notify DWQ of any problems with the system or prior to any
changes to the system or responsible party.
Print name: Thomas Young, Jr.
Title: President
Address: P.O. Box 14 Winnabow, NC 28479
Phone: 910-253-6611
Signature:
Date: 4-/- /a- O5
Note: The legally responsible party should not be a homeowners association unless more than 50% of the lots have been sold and
a resident of the subdivision has been named the president.
1, r 1 , a Notary Public for the State of � lry- �Lk 0j 'n Ck
County of , do hereby certify thato 11.tl a3r.
Personally appeared before me this _� day of k Dp , and acknowledge the due
Execution of the foregoing wet detention basin maintenance requirements. Witness my hand and official seal.
(taO TA'z? Y
P UB00 _U
-•�.rnm,,. SEAL
Signature �l . __t
My commission expires
Form SWU-102 Version 3.99 Page 4 of 4